Chapter 7 The Nervous System
General overview of the nervous system functions Sensory input (info travels in along afferent pathways) Integration (information is processed) Sensory neurons Spinal cord and brain Motor output (info results in a response, travels along efferent pathways) Stimulation of muscle and glands
General Overview
Nervous Tissue 2 kinds of cells neurons supporting cells: glia or neuroglia = nerve glue
CNS Neuroglia astrocytes microglia phagocytes: dispose of debris ependymal cells barrier between nerves and capillaries help circulate cerebrospinal fluid (CSF) oligodendrocytes produce myelin sheaths on CNS nerve fibers
CNS Neuroglia blue = nerve
PNS also has neuroglia Schwann cells - form myelin sheaths on PNS nerve fibers Satellite cells cushion PNS nerves
PNS Neuroglia
Neurons specialized cells that transmit messages cell body Nissl substance rough ER neurofibrils intermediate filaments
Nerve Anatomy: Processes dendrites convey incoming messages many per cell axons conduct messages away from cell body one per cell axon terminals
Nerve Anatomy axon terminal can connect to another neuron synapse = junction between neurons gap =?
Nerve Anatomy myelin: whitish, fatty, waxy protects and insulates fibers increases rate of impulse transmission Schwann cells - PNS nodes of Ranvier Oligodendrocytes - CNS
Schwann Cells & Nodes of Ranvier
Peripheral nerve regeneration is assisted by the Schwann cells
Multiple Sclerosis myelin sheaths gradually destroyed loss of muscle control
Nerve Anatomy nuclei: clusters of cell bodies in CNS ganglia: clusters of cell bodies in PNS tracts: bundles of fibers in CNS nerves: bundles of fibers in PNS white matter: myelinated fibers in CNS gray matter: unmyelinated fibers in CNS
Neurons can be classified by function
Neurons can be classified by structure based on # of processes that extend from the cell body
Nerve Physiology Overview:
If neurons are excitable cells What does this mean? How are they different from other cells in the body? Have we talked about a model in another cell for propagation of an impulse?
The cell membrane is where all the action occurs. Remember the chemical composition of the cell membrane? How does the chemical composition promote a separation of ions? Which ions are in greater concentration inside the cell? Outside the cell?
So far we know the following: For an inactive nerve cell: Intracellular fluid contains a high concentration of K+ Extracellular fluid contains a high concentration of Na+ Inside of cell has fewer cations than outside therefore the membrane is polarized
In a resting neuron Na+ cannot normally diffuse through membrane What would happen if the cell membrane were freely permeable?
When a neruon is stimulated Na+ gates open and Na+ diffuses into where? the polarity of the membrane is changed graded potential: membrane is depolarized in one area
If stimulus is strong enough action potential (nerve impulse) is generated long distance signal all or none propagates over entire axon
Action Potential
Repolarization Na+ rushing into cell triggers another change in membrane permeability membrane is no longer permeable to Na+, but IS permeable to K+ K+ diffuses out of the cell rapidly restores electrical conditions until restored, neuron cannot conduct impulse
Repolarization
After repolarization how do Na+ and K+ get back to original resting ionic conditions?
Saltatory conduction saltare = dance, leap myelin sheaths insulate membrane no current flow nerve impulse jumps from node to node fast!
What happens at the synapse? conduction of electrical impulse to another nerve via a neurotransmitter if enough neurotransmitter is released, action potential is generated electrochemical electro = transmission down neuron membrane chemical = transmission at synapse
What is happening when hands get cold? foot goes numb?
Lab Exercise 13 Turn in: Activities 1, 2, 3 Review Sheet on pp. 291-294